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    <title>Document</title>
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    <script src="//cdnjs.cloudflare.com/ajax/libs/socket.io/2.2.0/socket.io.js"
        integrity="sha256-yr4fRk/GU1ehYJPAs8P4JlTgu0Hdsp4ZKrx8bDEDC3I=" crossorigin="anonymous"></script>
    <script type="text/javascript" charset="utf-8">
        var socket = io('/', { transports: ['websocket'] });
        socket.on('connect', function () {
            socket.emit('my event', { data: 'I\'m connected!' });
        });
    </script>
    <h3>You need to access /flag at flask.net:5000 to solve</h3>
    <p>Good luck!</p>
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